Circulation and Gas Exchange

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• Circulation and Gas Exchange
• Chapter 42

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Overview Trading with the Environment

• Every organism must exchange materials energy
  with environment
• Exchanges ultimately occur at the cellular level

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• In unicellular organisms, exchanges occur
  directly with environment

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In multicellular organisms, direct exchange with
environment not possible with all internal
cells Diffusion always at cellular level
BUT diffusion over long dist (lung to internal
cells) too slow Therefore developed
physiological systems specialized for transport
(circulatory) exchange (respiration)
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Concept 42.1 Circulatory systems reflect
phylogeny

• Diffusion alone not adequate for transporting
  substances over long distances within animals
• Therefore complex animals have internal transport
  systems (circulatory systems) that circulate
  fluid connect the organs of exchange with the
  body cells for exchg

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Invertebrate Circulation

• The wide range of invertebrate body size form
  plus differences in environmental pressures
  diversity in circulatory systems

Gastrovascular cavities
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Open and Closed Circulatory Systems

• Complex animals with many cell layers have
• - open circulatory system
• - closed circulatory system
• Both have 3 components in common
• 1. circulatory fluid (blood or hemolymph
• 2. set of tubes (blood vessels)
• 3. muscular pump (heart provides pressure
• to move
  fluid)

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• In insects, other arthropods, molluscs blood
• bathes organs directly in open circ system
• no distinction between blood interstitial
  fluid
• general body fluid hemolymph

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• Closed circulatory system blood confined to
  vessels
• distinct from interstitial fluid
• Closed systems more efficient at transporting
• circ fluids to tissues cells (worm is an
  example)

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Vertebrate Circulation

• Humans other vertebrates blood flows in
• closed circulatory system (blood vessels 2-
  4-chambered
• heart) cardiovascular system
• - arteries carry blood to capillaries, sites of
  
• chemical gas exchange
  between blood
• interstitial fluid (single
  cell layer that gas exchanges)
• - veins return blood from capillaries to heart

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Fishes

• 2 main chambers ventricle atrium
• Blood pumped from the ventricle travels to the
  gills, where it picks up O2 and disposes of CO2

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Amphibians

• Frogs and other amphibians have a three-chambered
  heart 2 atria 1 ventricle

R atrium
L atrium
Ventricle
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Reptiles
Reptiles have double circulation, with a
pulmonary circuit (lungs) and a systemic circuit

• One can say that the reptile heart has 3
  chambers, 2 atria 1, partially divided,
  ventricle. Or one may argue that reptiles have
  4-chambered hearts with 2 atria 2 ventricles,
  but the wall between the ventricles is incomplete.

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Mammals and Birds

• In all mammals birds, ventricle divided
  into separate R L chambers
• L side pumps receives only
  O2-rich blood
• R side receives pumps only O2-poor blood

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• A powerful four-chambered heart was an
  essential adaptation of the endothermic way of
  life characteristic of mammals and birds
• Endotherms need 10x
• energy as equal-sized
• ectotherm so must
• deliver more via blood

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Concept 42.2 Double circulation in mammals
depends on anatomy pumping cycle of heart

• The human circulatory system serves as a model
  for exploring mammalian circulation

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Mammalian Circulation The Pathway

• Heart valves dictate a one-way flow of blood
  through the heart
• Blood begins its flow with R ventricle pumping
  blood to lungs
• In lungs, blood loads O2 unloads CO2
• O2-rich blood from lungs enters heart at L
  atrium into L ventricle where then pumped to
  body tissues
• Blood returns to heart at R atrium

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The Mammalian Heart A Closer Look

• provides a better understanding of dbl circ

Valves
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• Cardiac cycle
• - contraction, or pumping, phase systole
• - relaxation, or filling, phase diastole

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Heart sounds, heard with stethoscope, caused by
closing of valves.
lub-dup, lub-dup
Lubclose AV Dubclose semilunar
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Heart murmur defect in valve detectable as a
hissing sound when blood squirts backward through
it
Rheumatic fever can cause
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• Heart rate pulse beats per minute
• Cardiac OP volume blood pumped into systemic
• circ per minute
• Stroke vol amt blood pumped by L ventricle
• per contraction
• ________________________________________
• Av stroke vol 75 ml
• Av ht rate ..70/min
• Cardiac OP 75 70 (5,250 ml) 5.25 L/min

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Hearts Rhythmic Beat

• Cardiac muscle stims self contract without
  signal from nervous syst
• Pacemaker influenced by nerves, hormones, body T,
  exercise

Impulses during cardiac cycle can be recorded as
an electrocardiogram (ECG or EKG)
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Concept 42.3 Physical principles govern blood
circulation

• Structure/function arteries, veins,
  capillaries
• Velocity blood flow slowest in capillary beds

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• - arteries thick wall muscle
• - veins blood flow result muscle action valves

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- Exchange materials gases at capillaries - BP
at capillaries pushes fluid out into tissues
5,000
4,000
3,000
Area (cm2)
2,000
1,000
0
50
40
Velocity (cm/sec)
30
20
10
0
120
Systolic pressure
100
80
Pressure (mm Hg)
60
Diastolic pressure
40
20
0
Venae cavae
Veins
Venules
Capillaries
Arterioles
Aorta
Arteries
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• Fluid in tissues 85 reenters at venous end
• Remaining 15 returned via lymphatic system

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• Critical exchange between blood interstitial
  fluid
• takes place across thin endothelial walls
  capillaries
• Diff between BP p drives fluids out capillaries
  at arteriole end into capillaries at venule end

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Fluid Return by the Lymphatic System

• The lymphatic system returns fluid to the body
  from the capillary beds
• This system role in body defense
• Fluid reenters the circulation directly at the
  venous end of the capillary bed indirectly
  through the lymphatic system

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Concept 42.4 Blood is a connective tissue with
cells suspended in plasma
5 types Leukocytes
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Cellular Elements

• Suspended in blood plasma
• - red blood cells (erythrocytes) transport O2
• - white blood cells (leukocytes) body defenses
• - platelets frags cells involved in
  clotting

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Stem Cells Replacement of Cellular Elements

• pluripotent stem cells in red marrow of bones

erythropoietin
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Blood Clotting

• Cascade rxs (fibrinogen to fibrin) clot

hemophilia thrombus
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Cardiovascular Disease

• disorders of heart blood vessels
• account for gt half deaths in United States

Artheroscloresis accumulation cholesterol in
arteries
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• Chlosterol transported as lipidprot particles
• LDL (low density lipoprot) BAD cholesterol
• HDL (high density lipoprot) GOOD cholesterol
• Satd fats ? tendency artherosclerotic plaques

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• Hypertension, or high blood pressure, promotes
  atherosclerosis and increases the risk of heart
  attack and stroke
• A heart attack is the death of cardiac muscle
  tissue resulting from blockage of one or more
  coronary arteries
• A stroke is the death of nervous tissue in the
  brain, usually resulting from rupture or blockage
  of arteries in the head (can be side effect of
  heart attack)

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Concept 42.5 Gas exchange occurs across
specialized respiratory surfaces

• Gas exchange uptake O2 from environment
  discharge CO2 (from cell resp) to environment
• Animals require large, moist respiratory surfaces
  for adequate diffusion of gases between their
  cells the respiratory medium. air for
  terrestrial animals and water for most aquatic
  animals

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CO2
O2
Respiratory medium (air or water)
Respiratory surface
Organismal level
Circulatory system
Cellular level
Energy-rich fuel molecules from food
ATP
Cellular respiration
Structure of respiratory surface depends on
size of organism whether it lives in water
or on land
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• A. Water Habitat

- Have gills outfoldings of body surface
suspended in water - Water O2 low so special
processes to ? efficiency of exchg
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B. Terrestrial Habitat

• Tracheal system of insects consists of tiny
• branching tubes that penetrate the body

The tracheal tubes supply O2 directly to body
cells
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Lungs

• Most terrestrial vertebrates have internal lungs

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• system of branching ducts conveys air to lungs
• Air inhaled through the nostrils passes through
• pharynx into trachea, bronchi, bronchioles,
• dead-end alveoli, where gas exchange occurs

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• Mammals ventilate their lungs by neg pressure
• Inhale ?vol lung pulls air into the lungs
• Exhale musc relax elastic fibers retract
  lung

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Main breathing control center in brain which
regulates rate depth of breathing in response
to pH changes in Cerebrospinal fluid
Sensors in aorta carotid arteries monitor O2
CO2 concentration in blood exert 2ndary
control over breathing
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• Gases diffuses from higher partial pressure
  (conc) to lower partial pressure

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Oxygen Transport

• Hemoglobin reversibly binds O2
• - loads O2 in lungs
• - unloads it in other parts body

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Drop in pH lowers affinity of hemoglobin for O
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Carbon Dioxide Transport (mostly as HCO3)
CO2 diffuses into Red blood cells where H2O
forms carbonic acid which dissoc into H
HCO3- H binds to Hemoglobin HCO3- diffuses
into plasma carried to lungs In lungs,
reverse occurs
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CO2 from respiring cells diffuses into blood
plasma then into red blood cells
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CO2 from tissues carried as HCO3- in plasma of
blood released in lungs
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Baby steals O2 from moms blood